t3OLID POLYIODIDES Or RWBIDIUM
633
REFERENCES (1) FRANKFORTER AND COHEN: J. Am. Chem. SOC.98, 1103-34 (1914). (2) FRANKFORTER AND FRARY: J. Phys. Chem. 17, 402-73 (1913). AND TEMPLE: J. Am. Chem. SOC.87,2697-716 (1915). (3) FRANKFORTER (4) GINNINQS AND CHEN:J. Am. Chem. SOC.62, 2282-6 (1930). AND DIES: J. Am. Chem. SOC.67, 1 0 3 8 4 (1935). (5) GINNINQS (6) GINNINQS, HERRINQ, AND WEBB:J . Am. Chem. SOC.66, 8758 (1933). (7) GINNINQS AND ROBBINS: J. Am. Chem. SOC.63, 3765-9 (1931).
SOLID POLYIODIDES OF RUBIDIUM' H. W. FOOTE
AND
MICHAEL FLEISCHER
Department of Chemistry, Yale University, New Haven, Connecticut Received June W , 1089
Rubidium triiodide was first prepared by Wells and Wheeler (9). Solubility results in water solutions a t 25°C. by Foote and Chalker (5) and freezing point measurements by Briggs and Patterson (2) on rubidium iodide-iodine mixtures show that this is the only binary polyiodide of rubidium a t temperatures of 25°C. or above. However, the work of Abegg and Hamburger (1) by the solubility method with benzene as solvent indicated the existence of three compounds which they believed to be RbIa, RbI,, and RbIs. In the light of the results obtained in this laboratory on the polyiodides of potassium (3) and cesium (4), it seemed likely that the two higher polyiodides of rubidium reported by Abegg and Hamburger were actually ternary compounds containing benzene of crystallization. We have therefore studied the systems rubidium iodideiodine-benzene and rubidium iodide-iodine-toluene a t 6' and 25°C. The experimental procedure and the purification of materials have been described (3). Rubidium iodide was prepared from a pure sample of the nitrate by fusion in platinum with oxalic acid and subsequent evaporation with excess hydriodic acid. The material was twice recrystallized as the triiodide, and was converted to the iodide by gentle heating. The system rubidium iodide-iodine-toluene proved to be very simple (see table 1). No solvated compounds exist, as shown by closed-tube tests on residues, and both the iodide and triiodide are insoluble in the solvent, so that the composition of all residues could be calculated from the known original charges and the analytically determined iodine conThis article is based on a thesis presented by Michael Fleischer to the Faculty of the Graduate School of Yale University in partial fulfillment of the requirements for the degree of Doctor of Philosophy, June, 1933.
634
H.
w.
FOOTE AND MICHAEL FLEISCHER
centration in the solution. As found by the earlier workers by other methods, the triiodide is the only stable binary compound. The average of the six results on rubidium triiodide is 54.51 per cent available iodine, in excellent agreement with the theoretical value, 54.45 per cent. Qualitative tests a t the iodine end of the system rubidium iodideiodine-benzene showed that the residues were solvated. The system proved to be rather perplexing and a large number of determinations was carried out. Considerable trouble was caused by persistent metastable
TABLE 1 The system rubidium iodide-iodine-toluene ~~
SBBIAL NO.
IODINE I N SOLUllON
~
AVAILABLE IODINE IN RBBIDUE
t =
3 4 5
0.76 1.02 7.03
6 7
10.19 10.33
'
EOLID PHABBB PRWENT ~
6°C.
54.57 54.49 54.47
1
60'69 90.33
1
RbIa
RbIs and
12
~
t
11 12 13
=
25'C.
7'91 48.74 49.33
8 9 10 1.83 14.90 15.07
54.54 ~
RbI and RbIa
}
RbIa
equilibria. It was found necessary to grind the solids very fine, and to shake the bottles vigorously before placing them in the thermostat. The solubility results show that there are four points of constant solution composition with varying solid phase composition a t each temperature; three compounds are present, two of which are solvated. The results a t both temperatures are given in table 2. All compositions are in weight per cent. As indicated in table 2, three different methods were used to obtain the compositions of the solid residues in different parts of the system. When
TABLE 2 The system rubidium iodide-iodirw-benzerw
1
1
BOLIDREBIDUE
i
YININO
i COYPOSI-
SOLIDB PRESENT
TION OF
2 = 6'C. wun'ght per cent
weight per cent
weight per cent
0.0 0.0
2
0.17 0.18
91.56 50.93
3 4
0.61 3.71
46.00 45.65
r54.00
M .35
0.0 0.0
5 6
4.08 4.07
26.1 22.1
57.6 58.2
16.3 19.7
7 8 9 10 11 12 13 14
4.24 4.49 4.99 5.34 5.70 5.75 5.97 6.92
16.82 16.87 16.23 15.80 15.79 15.90 16.27 16.18
62.93 62.50 62.46 60.86 62.83 59.18 60.47 61.63
20.25 20.63 21.31 23.34 21.38 24.92 23.24 22.19
15 16 17
6.98 7.00 6.98
16.1 15.4 15.0
60.3 61.4 62.9
23.6 a3.2 22.1
18 19
20 21 22 23
7.17 7.58 7.88 7.95 8.15 8.53
14.43 13.27 13.32 13.90 13.55 14.13
65.89 62.26 62.82 66.76 64.83 63.22
19.68 24.47 23.86 19.34 21.62 22.65
24 25 26
8.72 8.71 8.69
14.8 12.0 8.8
63.5 70.3 78.2 - - ___
0.99 6.05 8.06
45.49 45.70 45.76
54.51 54.30 54.24
1)
RbI and RbIs
RbIa and Rb17.4CsH~
21.7 17.7 13.0 ~
t
30 31 32
1)
wun'oht p a cent
8.44 49.07
1
=
25T.
0.0 0.0 0.0
a
I}
RbI,
* a, residue unsolvated, composition calculated tm in toluene system; b, composition of residue calculated algebraically; c, composition of residue determined by analysis. 636
636
H. W. FOOTE AND MICHAEL FLEISCHER
I 1
TABLE %Concluded
METHOD OF DITERMINING COMPOIJI-
UOLID R W D U E
BERIAL IODINB I N NO. ~8OLWCION~
RbI
1 *gk;le I
-
Bsmne
BOLIDB PBEBENT
'IoN OF BEBIDUE
t 25°C.--Conlinued weight pa7 em;
what pa7
cent
ohat
waighl pa cent
pa cent
33 34
9.19 9.13
41.3 16.8
55.1 59.1
3.6 24.1
35 36 37
9.68 9.79 10.04
15.69 16.59 15.55
63.91 64.60 61.54
20.40
38 39
10.92 10.88
16.2 15.2
60.0 62.4
23.8 22.4
40 41 42 43
11.61 12.85 13.44 13.65
13.92 14.18 14.11 13.94
66.86 66.34 64.78 64.85
19.22 19.48 21.11 21.21
44 45 46
14.13 14.15 14.31
12.7 10.4 3.2
68.6 74.2 92.1
18.7 15.4 4.7
b b
} RbIa and Rb11.4C6He
19.81 22.91
the residue was unsolvated, the composition of the residue wm calculated as in the toluene system. When two solid phases, one or both of which was solvated, were present, the composition of the solid residue was calculated algebraically. When the solid residue consisted of one of the ternary compounds, it was analyzed for available iodine and for rubidium iodide, after being dried between filter papers. The solubility data in table 2 show that three compounds are present a t each temperature. The presence of rubidium triiodide is shown by the results, the average of the five runs in which it was the solid phase being 54.28 per cent available iodine in the residue (theoretical value, 54.45 per cent). The molecular composition of the ternary compound lower in iodine, as determined from the analyses in table 2, is given in table 3(A). Since the solid analyzed always contained free iodine derived from the evaporation of mother liquor, the molecular ratios are always high for available iodine. The results in table 3(A) indicate that the formula of the ternary compound is RbI.BI.4CsHe. However, it is apparent that if the ratio RbI :CsHs in the solid phase is known, the composition of the solid phase can be calculated as in the toluene system. Such a calculation has been
637
SOLID POLYIODIDES OF RUBIDIUM
carried out for each experiment in which the compound was present, assuming the ratio RbI:CeHe to be 1:4. The results of this calculation, given in table 3(B), confirm the formula above, the ratio 1:RbI being, as expected, much closer to 6 than the ratio derived from the direct analyses. The molecular composition, calculated from the analyses in table 2, of the ternary compound higher in iodine is given in table 4(A). From the analyses, the ratio 1:RbI appears a t first glance to be 8:l. However, it must be remembered that the solutions from which the solid was removed for analysis were high in iodine content, so that even a small amount of TABLE 3 Composition of ternary con und lower i n iodine (B)
(A) Y O L E C U U R RATIO8 PROM ANALYSES IN TABLE
a
8ERIAL NO.
RbI
7 8 9 10 11 12 13 14 35 36 37 Average . .
.I
:
*:2kiPele : CsHe
-
REMIDUE CALCULATED ABBUYINO.
RbI:CeHe
1:4
Available
RbI
iodine
Ratio
1:RbI
d o l t pa cent
might percent
1 .o 1.0 1.0 1 .o 1.0 1 .o 1.0 1.0 1.0 1 .o 1 .o
6.26 6.20 6.44 6.44 6.66 6.22 6.22 6.37 6.82 6.52 6.62
3.27 3.33 3.57 4.02 3.68 4.27 3.89 3.73 3.54 3.08 4.01
16.22 16.34 16.38 15.74 16.33 16.57 17.07 16.91 15.93 16.43 16.09
59.91 59.62 59.53 59.53 59.64 59.05 57.82 58.23 60.65 59.40 60.23
6.18 6.10 6.08 6.33 6.11 5.96 5.67 5.76 6.37 6.05 6.26
1 .O
6.43
3.67
16.36
I
59.42
6.08
16.50
1
59.18
6.00
Theoretical for RbI.61.4CaHs.. , . . . , . . , , ,
evaporating mother liquor would deposit considerable free iodine. Allowing for the fact that the analyses are to be expected to show an excess of iodine, the formula of the compound would appear to be RbI.71.4CsHs. If the ratio RbI:C& is taken as 1:4 and the composition of the residue is calculated, the results given in table 4(B) are obtained. These confirm the formula above with 1:RbI = 7:l. Thus, the two ternary compounds have the formulas RbI. 61.4CsHs and RbI .71.4CJIe, differing by one atom of iodine. No ternary compounds with analogous formulas have been reported in the literature, but we have obtained a very unstable compound KSCK.61.4CsHs (6). It is rather interesting to note that the compounds CsI 91 2C& K I . 81.3CSH6, and RbI 71.4C& e
e
638
H. W. FOOTE AND MICHAEL FLHISCHER
m e r by having one atom of iodine less and one molecule of benzene more, in order. Recently Grace (8) published a study of the system rubidium iodideiodine-benzene a t 25°C. He also found two solvated compounds, but gave their compositions as RbI .61.2CJIo and RbI .SI. 2CJ36. It seems probable that the discrepancy in benzene content is due to the different methods used by Grace and by UF. to prepare the solids for analysis. His method consisted in placing the material in an isoteniscope and pumping off slowly until the dissociation pressure of the compound, determined in a preliminary experiment, was reached. Grace's results therefore give a lower limit to the benzene content. Our own method consisted in TABLE 4 Composition of tarnary corn und higher in iodine
no.
a
RbI
: QHe
:
RlDLllDDll W L A T I P D AMUXINQ
RbI:Ch"
RbI ocisat pa
18 19 #)
21 22 23 40 41 42 43 Average. . .
-
(B)
(A) YOLllCUIdB BATIOI) TROY mALTBml) n TABLE
1.0 1.0 1 .o 1.0 1.0 1.0 1.0 1.0 1.0 1 .o
7.64 7.85 7.89 7.95 8.01 7.48 8.04 7.83 7.68 7.78
3.71 5.02 5.28 3.74 4.34 4.36 3.75 3.74 4.07 4.14
14.68 14.95 15.04 14.89 14.68 15.13 14.52 14.83 14.60 14.78
1.0
7.82
4.22
14.78
Theoretical for RbI.71.4CsHs... . . . . . . . . .
15.02
1:4
Available iodine
Ratio
1:RbI
wight pa catrl
63.73 63.80 62.84 63.12 63.73 62.70 64.14 63.37 63.94 63.49
7.27 7.29 6.99 7.09 7.27 6.92 7.39 7.16 7.33 7.19 7.19
62.87
7.00
drying the solid between filter papers until decomposition had just begun, as told by a lightening of the color of the compound, then analyzing immediately. Our results should also give a lower limit to the benzene content, but it seems likely that Grace's material had lost more benzene of constitution than had ours before analysis. It is difficult to decide the correct degree of solvation for such compounds, which are removed from solutions in volatile solvents and which lose their solvent of crystallization so readily. Our formulas are based on twenty-one analyses of the two compounds; Grace's formulas on four. The ratio 1:RbI found by Grace for the ternary compound higher in iodine was 8, which is in excellent agreement with our analyses of the
639
SOLID POLYIODIDES OF RUBIDIUM
same compound. Nevertheless, as we have pointed out, this ratio appears incorrect, because of contamination of the sample with free iodine deposited by evaporating solvent. At 25°C. the compound is stable only in contact with solutions containing over 11 per cent by weight of iodine, and it is impossible to dry the solution without contamination. The data in table 4(B) indicate also that the higher ternary compound has the ratio 1:RbI = 7, not 8. The dissociation pressure of rubidium triiodide has been obtained from the solubility results a t 6" and 25°C. by the method previously explained (4). The values of C/CO for both solvents a t both temperatures Showing the r a t i o
C/CQ
TABLE 5 d 6' and 86°C. for both solvents
1
aoum -P
~
IODIXEINOOLUTION
Toluene; t = 6°C. I* and RbI:. . . . . . . . . . . . . . . . . . . . . . . . RbIg and R b I . . ....................
-
.I
weight pa a t
10.26 0.20
1
3.98 (CO) 0.0727 (c)
1
2.85 (CO) 0.0539 (c)
mds per car1
I
1
0.0182
Benzene; t = 6°C.
..I 1
1, and RbIs.4CdIs.. . . . . . . . . . . . . . . . . . . RbI: and R b I . . . . . . . . . . . . . . . . . . . . . .
8.71 0,175
I
0.0189
Toluene; t = 25°C. It and RbIs. . . . . . . . . . . . . . . . . . . . . . . . . . . RbIg and R b I . . . . . . . . . . . . . . . . . . . . . . . .
'i::
~
6.21 ( C Q ) 0.146 (c)
0.0234
Benzene; t = 25°C. I, and RbI,.dC&. . . . . . . . . . . . . . . . . . . . RbIg and R b I . . . . . . . . . . . . . . . . . . . . . . . . ~
14.20 0.37
~
4.84 ( C Q ) 0.114 (c)
1
~~
0.0236
are given in table 5. The agreement is within the error of the solubility determinations. From these values of C / C O the dissociation pressure of rubidium triiodide is calculated to be 0.00101 and 0.00736 mm. a t 6" and 25"C., respectively, and the heat of dissociation is -17.2 kg.-cal. In these calculations the vapor pressure of iodine has been assumed to be 0.0546 and 0.313 mm. at 6" and 25"C., respectively. These vapor pressures were obtained by interpolation from the Znternational Critical Tables. The values would be changed slightly if we had used the "best" values for the vapor pressure of iodine, 0.0556 and 0.309 mm. a t 6"and 25"C., recently given by Gillespie
640
H. W. FOOTE AND MICHAEL FLEISCHER
and Fraser (7). The older values were used so that the dissociation pressures calculated would be consistent with those given in our earlier papers. SUMMARY
The systems rubidium iodide-iodine-toluene and rubidium iodideiodine-benzene have been studied at 6' and 25°C. The binary compound rubidium triiodide is the only compound stable a t both temperatures in the toluene system. In the benzene system two ternary polyiodides, RbI. 61. 4CsH6and RbI .71.4C&, are stable phases a t both temperatures. The dissociation pressure of rubidium triiodide a t both temperatures has been calculated from the solubility results. REFERENCES
(1) (2) (3) (4) (5) (6) (7) (8) (9)
ABEGGA N D HAMBURGER: Z. anorg. Chem. 60,403 (1906). BRIGGSA N D PATTERSON: J. Phys. Chem. 36, 2621 (1932). FOOTE A N D BRADLEY: J. Phys. Chem. 36, 673 (1932). FOOTE, BRADLEY, AND FLEISCHER: J. Phys. Chem. 37, 21 (1933). FOOTE AND CHALKER: Am. Chem. J. 30, 561 (1908). FOOTE AND FLEISCHER: Unpublished data. GILLESPIEAND FRASER: J. Am. Chem. SOC.68, 2260 (1936). GRACE:J. Phys. Chem. 37, 437 (1933). WELLSAND WHEELER:Am. J. Sci. 44, 43 (1892).
ADDITION COMPOUNDS OF IODINE WITH ALKALI BROMIDES AND THIOCYANATES H. W. FOOTE
AND
MICHAEL FLEISCHER
Department of Chemistry, Yale University, New Haven, Connecticut Received June $0, 1969
Addition compounds of iodine with the iodides of potassium (4), ammonium (5), rubidium (7), and cesium (6) have been studied in this laboratory by the solubility method. It seemed desirable to extend our work to study the addition of iodine to alkali bromides and thiocyanates in order to widen our'knowledge of the stability relations of this type of addition compound. We used benzene and toluene as solvents, since our previous work had shown that only binary polyiodides are formed with toluene as solvent, but that there are a number of solvated ternary compounds composed of an iodide, iodine, and benzene. 1 This article is taken in part from a dissertation submitted by Michael Fleischer to the Faculty of the Graduate School of Yale University in partial fulfillment of the requirements for the degree of Doctor of Philosophy, June, 1933.
